Method and system for preheating epoxy coatings for spray application

ABSTRACT

A method and system for the spray application of epoxy materials is provided. The system includes a dual walled tank structure as a reservoir for containing and preheating the epoxy materials in preparation for mixing and spray application. Each component of the epoxy material is preheated before the components are mixed. After preheating, the components are then mixed together and spray applied. The method and system of the present invention provides a high quality spray applied epoxy coating while reducing equipment down time and cleaning.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 11/275,952, filed Feb. 7, 2006 which is related to and claimspriority from earlier filed U.S. Provisional Patent Application No.60/672,694, filed Apr. 19, 2005.

BACKGROUND OF THE INVENTION

The present invention relates generally to a system for the sprayapplication of epoxy materials. More specifically, the present inventionis directed to a method and system for preheating the various componentsof epoxy materials prior to their being mixed in order to reduce theirviscosity thereby facilitating spray application thereof.

Generally, epoxy coatings are well known in the art and due to theirexceptional durability and structural properties epoxy based protectivecoatings have gained commercial acceptance as protective and decorativecoatings for use on a wide variety of materials. For example, epoxybased protective coatings represent one of the most widely used methodsof corrosion control. They are used to provide long term protection ofsteel, concrete, aluminum and other structures under a broad range ofcorrosive conditions, extending from atmospheric exposure to fullimmersion in highly corrosive environments. Further, epoxy coatings arereadily available and are easily applied by a variety of methodsincluding spraying, rolling and brushing. They adhere well to steel,concrete and other substrates, have low moisture vapor transmissionrates and act as barriers to water, chloride and sulfate ion ingress,provide excellent corrosion protection under a variety of atmosphericexposure conditions and have good resistance to many chemicals andsolvents. As a result, numerous industries including maintenance,marine, construction, architectural, aircraft and product finishing haveadopted broad usage of epoxy coating materials.

The most common material utilized in the epoxy coating industry today isa multi-part epoxy material. In general the epoxy includes a first baseresin matrix and at least a second catalyst or hardener, although othercomponents such as a pigment agent or an aggregate component may also beadded. While the two parts remain separate, they remain in liquid form.After the two parts are mixed together, they begin a curing process thatis typically triggered by exposure to heat, humidity or a ultra-violetlight source, whereby the mixed material quickly begins to solidify. Theresin base and the catalyst are typically highly viscous in consistencyand when mixed, generally having a paste like consistency.

The difficulty found in the prior art is that while epoxy has highlydesirable characteristics as a finished coating, the preferred method ofapplication is spray application. When attempting to spray apply anepoxy, two drawbacks are encountered. First, the material cannot bemixed in large batches prior to application because of the short potlife of the material. Accordingly, it must be mixed on an as neededbasis immediately prior to spray application. Second, the naturallyviscous consistency of the mixed epoxy material is not well suited forspray application. To thin the epoxy to the consistency required fortypical prior art spray application, the epoxy must be loaded with alarge percent by volume of solvent. Such a solvent typically containshigh level of volatile organic compounds (VOC) whose primary function isto lower viscosity thereby providing a consistency suitable for sprayapplication with conventional air, airless and electrostatic sprayequipment. The addition of the solvent to the epoxy coating material inturn greatly increases the VOC content of the epoxy coating material andreduces the build thickness of the finished and cured coating.

In view of the above, the problem with spray application of epoxycoating materials becomes two fold. First, there is a growing emphasison compliance with government environmental and health hazardregulations, which in turn has prompted coating material manufacturersand end users to evaluate new coating technologies. The Clean Air Actsets limits on both the type and amount of VOC content found in coatingmaterials and has resulted in research directed to higher solids,solventless and waterborne protective coating systems. As a result ofsuch research, the newer epoxy materials are either highly viscousresulting in a poor quality finish when spray applied or too thin toproduce the type of high build coating that is normally expected fromspray applied epoxy coatings.

While many processes and techniques have been proposed in the prior forthe spray application of epoxy coating materials to substrates, priorart spray processes are directed to the reduction of material viscositythrough the use of solvents. In most cases, such spray operationsoperate with materials having a low viscosity on the order of 100 poiseand utilize a relatively low application pressure on the order of nomore than about 100 psi.

Therefore, there is a need for a system and method of spray applicationof high molecular weight, highly viscous polymeric thermally curedmaterials at elevated temperature. There is a further need for a systemand method of applying epoxy coating materials that eliminates orreduces the need for solvent loading while also providing a mixed epoxyproduct that has a consistency that is suitable for spray application.There is still a further need for a system for spray applying an epoxymaterial that is capable of continuous duty wherein a low viscosityepoxy can be spray applied without a high level of equipment down timeor recycling time. Simply stated, the art is devoid of any proventechnique for spraying high molecular weight epoxy coating materials ofthis character.

BRIEF SUMMARY OF THE INVENTION

In this regard, the present invention provides for a method and systemcapable of reducing the viscosity of epoxy materials in preparation ofspray application without the need of thinning through the addition ofVOC solvents. In the method and system of the present invention thecomponent parts of the epoxy material are preheated before they aremixed, thereby achieving a large reduction in the material viscositywithout requiring thinning of the material or the addition of solvents.

The present invention provides for a dual walled tank structure as areservoir for containing and preheating the epoxy materials inpreparation for mixing and spray application. The inner wall of the tankforms a storage reservoir in which the base resin is stored. The cavitybetween the inner wall and the outer wall in the dual wall constructionprovides a water jacket that surrounds the interior tank. Heatingelements are provided within the water jacket, which serve to heat thewater within the water jacket, which in turn heats the interior tank andthe resin stored therein. Preferably, the water jacket heats the resinto a discharge temperature of approximately between 150° F. and 160° F.Also within the scope of the present invention, the water jacket mayinclude in addition to plain water a simple soap or detergent additivethat is employed to flush the resin and catalyst lines after the sprayapplication is completed. In the prior art, the lines were traditionallyflushed using solvents creating a potentially hazardous condition whenapplying materials in closed environments. The present invention insteademploys a solvent free soap and water mixture thereby making the entireprocess solvent free.

It is important to note that in the preferred embodiment of the presentinvention, the heating of the resin takes place in two steps. In thefirst heating step, the resin in the tank is initially heated to atemperature that allows the resin to flow, but is well below theevaporation temperature of the various components within the resin. Thisprevents various chemical components within the base resin from flashingoff, thereby changing the chemical composition and characteristics ofthe resin. In a second heating step, as the resin is being pumped out ofthe storage tank it enters a series of heating coils that serve tocontain the resin in a closed environment while heating the resin to thedesired application temperature. In this manner, even if evaporationdoes occur, it is fully contained and all of the resin components aretransferred intact to the mixing nozzle. Similarly, if the catalyst wereheated to the target temperature range using the same method in an opencontainer, some of the components, such as ammonia, that are in thecatalyst would evaporate creating problems in the finished product.Since the catalyst cannot be heated in an open chamber another set ofcoils is provided that resides within the water jacket. The catalyst ispassed through these coils before mixing, as will be discussed in detailbelow, to also preheat the catalyst to the desired temperature range.

Yet another set of coils may be provided to facilitate the refilling ofthe resin tank while the machine is in operation. This coil extends fromthe exterior of the tank into the resin tank and allows the resin to bepreheated before it is deposited into the resin storage tank. Thisallows the resin tank to be periodically refilled without having to stopthe application of the material while waiting for the newly addedmaterial in the resin storage tank to preheat.

The resin is drawn from the resin storage tank by a resin pump afterbeing heated. The catalyst is push pumped by a second pump through thecatalyst heating coil. The resin and catalyst flows are then joined in athird mixing pump that mixes the two parts together and supplies thepressurized epoxy to a spray applicator for application onto the desiredsurface. The method and system of the present invention thereforeprovides a two-part epoxy mixture that is preheated and has a viscositythat is sufficiently low for spray application without the need for theaddition of solvent. The resulting coating has an improved build and ahigher structural value as compared to epoxies that were applied usingthe prior art systems and methods.

It is therefore an object of the present invention to provide a methodand system for the spray application of epoxy coating material. It is afurther object of the present invention to provide a method and systemfor the spray application of epoxy coating material while eliminatingthe need for thinning the material with VOC solvents. It is yet afurther object of the present invention to provide a method and systemfor the spray application of epoxy coating material by preheating thecomponent parts of the material in a closed environment before combiningand mixing the component parts thereby achieving a reduction in theviscosity of the epoxy material without the need for the addition of VOCsolvents. It is still a further object of the present invention toprovide a method and system for spray application of epoxy material thatis capable of preheating the material in a manner that substantiallyreduces the material viscosity while also being capable of nearcontinuous operational duty.

These together with other objects of the invention, along with variousfeatures of novelty, which characterize the invention, are pointed outwith particularity in the claims annexed hereto and forming a part ofthis disclosure. For a better understanding of the invention, itsoperating advantages and the specific objects attained by its uses,reference should be had to the accompanying drawings and descriptivematter in which there is illustrated a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which illustrate the best mode presently contemplatedfor carrying out the present invention:

FIG. 1 is a perspective view of a preferred embodiment system for thespray application of epoxy material in accordance with the disclosure ofthe present invention;

FIG. 2 is a cross-sectional vies of the system taken along line 2-2 inFIG. 1; and

FIG. 3 is a schematic view of the method and system of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Now referring to the drawings, a preferred embodiment of the system forspray application of epoxy coating materials is shown and generallyillustrated at 10 in the figures. It is important to understand thatwhile this preferred embodiment is shown for the purpose ofillustration, the system and method of the present invention may beaccomplished by using many different structural variations that arestill intended to be covered within the scope of the present invention.Further, for purposes of the present application, the term “sprayapplication” refers to breakup of the material into small particles ordroplets that are broadcast onto a substrate in a pattern, such as afan, sheet or cone pattern, that has a width at the point of depositionon the substrate that is many times the diameter of the spray nozzleopening. Spray application is therefore defined in a manner that is tobe distinguished from “flowing” or “extruding” where the material at thepoint of deposition has a dimension that is about the same a thedimension of the opening. Accordingly, as discussed above, the presentinvention is directed to a method and system for spray application ofhigh molecular weight polymeric thermal-cure epoxy materials, such asstructural epoxy, that handles the material at application temperatureand pressure without requiring solvents or the like to reduce viscosity.

Turning now to FIGS. 1 and 2, it can be seen that the system 10 of thepresent invention includes generally a heating tank 12, means forestablishing a flow of epoxy resin 14 through the heating tank 12, meansfor establishing a flow of catalyst 16 thought the heating tank 12,means for mixing the flow of resin and catalyst 18 to form a multi-partepoxy mixture and a discharge nozzle 20 for the spray application of theepoxy mixture onto a substrate surface.

The heating tank 12 is the principal element of the system 10 of thepresent invention. The heating tank 12 is constructed using a doublewall construction. The heating tank 12 includes an outer structural wall22 that encloses the entire assembly and serves to house and contain therequired heating elements of the system 10 of the present invention. Theouter tank wall 22 may be metallic or formed from a structural polymersuch as a reinforced fiberglass or the like. Further, the exteriorsurface of the outer wall 22 may be insulated to increase theperformance and energy efficiency of the overall system 10. Disposed onthe interior of the heating tank 12 is an inner wall 24 that isgenerally placed in spaced relation to the outer wall 22. The inner wall24 has inner surface 26 and an outer surface 28, wherein the said outerwall 22 and said outer surface 28 of said inner wall 24 cooperate toform a heating jacket 30 therebetween. In particular, the inner wall 24and outer wall 24 cooperate to form a chamber that is suitable toreceive and retain a heat transfer medium 32 thereby creating a heatingjacket 30. In the preferred embodiment, the heat transfer medium 32 iswater, although any fluid medium that is known in the art to be suitablefor the effective and efficient transfer of heat between objects may beused and still fall within the scope of the present invention.

The inner surface 26 of the inner wall 24 is formed in a manner thatcreates an interior chamber 34, which is surrounded on at least itsperimeter by the heating jacket 30. The interior chamber 34 issegregated from the heating jacket 30 and is formed to receive andretain the base resin material 36 therein. As will be described infurther detail below, the resin 36 within the interior resin chamber 34is preheated as a result of heat transfer to the interior resin chamber34 from the heat transfer medium 32 contained in the surrounding heatingjacket 30.

A means for heating 38 the heat transfer medium 32 is disposed withinthe heating jacket 30 and is in contact with the heat transfer medium32. The means for heating 38 the heat transfer medium 32 may include anysuitable heating means known in the art. For example, the heating means38 may be any direct heating means such as an electrical resistanceheating coil or a direct-fired fuel burner such as a natural gas,propane or oil fired burner. Similarly the heating means 38 may be anyknown means of indirect heating means. Generally for the purpose of thepresent invention, means for heating 38 the heat transfer medium 32encompasses any known device for imparting heat to the heat transfermedium 32. Further, within the scope of the present invention, the heattransfer medium 32 may include in addition to plain water a simple soapor detergent additive that is employed to flush the resin and catalystconduits 40, 42 lines after the spray application is completed. In theprior art, the lines were traditionally flushed using solvents creatinga potentially hazardous condition when applying materials in closedenvironments. The present invention instead employs a solvent free soapand water mixture thereby making the entire process solvent free.

As was stated above therefore, the heating jacket 30 provides a means bywhich the heat transfer medium 32 can facilitate a uniform and steadysupply of heat to preheat the resin 36 contained in the resin chamber34. In addition to having a heating means 38 within the heating jacket30, the present invention provides at least a resin heat transferconduit 40 and a catalyst heat transfer conduit 42, both of which aredisposed within said heating jacket 30. The resin heat transfer conduit40 is formed as a continuous piping conduit that has a an input end 44in fluid communication with said resin chamber 34 and an output end 46disposed on the exterior of the outer wall 22 of the heating tank 12.Similarly, the catalyst heat transfer conduit 42 is formed as acontinuous piping conduit that has an input end 48 in fluidcommunication with a catalyst reservoir 50 and an output end 52 disposedon the exterior of the outer wall 22 of the heating tank 12. The pipingconduit that extends between the input end and the output end of boththe catalyst and resin heat transfer conduits 42, 40 extends through theheating jacket 30. Further the piping conduit of both the resin andcatalyst heat transfer conduits 40, 42 may be formed in a manner thatprovides increased surface area in order to facilitate heat transferfrom the heating jacket 30 to the interior of the heat transfer conduits40, 42. To accomplish this, the resin and catalyst heat transferconduits 40, 42 may each be formed as a coil having several loops ofpiping that all pass through the heating jacket 30. Additionally, theouter surface of piping conduit may include other surface areaenhancements such as ribs or fins.

The operational portion of the system of the present invention includesmeans for establishing a flow of resin 14, means for establishing a flowof catalyst 16 and means for mixing 18 the flow of resin and catalyst inpreparation of discharge of the epoxy coating. In each case, in thepreferred embodiment the means for establishing the flow is preferably apump. The pump may be any type pump suitable for the transfer of fluidmaterials. In establishing a flow of resin, a resin pump 14 ispreferably connected to the output end of the resin heat transfer coil40 thereby drawing resin 36 from the resin chamber 34 and through theresin heat transfer coil 40. The flow of catalyst is established by acatalyst pump 16 that draws the catalyst from a catalyst reservoir 50and discharges the catalyst into the input end of the catalyst heattransfer conduit 42 thereby pushing the catalyst through the catalystheat transfer conduit 42. Both the flow of resin 54 and the flow ofcatalyst 56 are then discharged into a mixing pump 18 where the catalystand resin are mixed and discharged at an elevated pressure to a spraynozzle 20 for spray application of the mixed, multi-part epoxy. While aparticular pumping arrangement is disclosed, anyone skilled in the artcan appreciate that repositioning the various pumps by placing them atdifferent locations in the flow paths of the catalyst and resin wouldstill produce a device that would fall within the scope of the presentinvention.

It is important to note that in the preferred embodiment of the presentinvention the resin 36 and catalyst are both heated separately beforethey are mixed. In the prior art, when the two parts were mixed prior toheating, the applicator was faced with a tank full of activated materialthat has a relatively short pot life before hardening. Further, at theend of the application, any mixed material remaining in the tank waswasted. The present invention provides for the two components to beheated separately and then mixed thereby requiring that only the epoxymaterial that is needed be mixed.

Another important feature of the present invention is that the heatingof the resin 36 takes place in two steps. In the first heating step, theresin 36 in the resin tank 34 is initially heated to a temperature thatallows the resin 36 to reach a lowered viscosity and thereby flow, butis well below the evaporation temperature of the various componentswithin the resin 36. This prevents various chemical components withinthe base resin 36 from flashing off, thereby changing the chemicalcomposition and characteristics of the resin 36. In a second heatingstep, as the resin 36 is being pumped out of the resin tank 34 it entersthe resin heat transfer conduit 44 wherein the walls of the piping serveto contain the resin 36 in a closed environment while heating the resin36 to the desired application temperature of between approximately 150°F. and 160° F. In this manner, even if evaporation does occur, it isfully contained and all of the resin 36 components are transferredintact to the mixing pump 18. Similarly, if the catalyst were heated tothe target temperature range of between approximately 150° F. and 160°F. using the same method in an open container, some of the components,such as ammonia, that are in the catalyst would evaporate creatingproblems in the finished product. Since the catalyst cannot be heated inan open chamber a catalyst heat transfer conduit 42 is provided thatresides within the heating jacket 30. The catalyst is passed through thecatalyst heat transfer conduit 42 before mixing, to also preheat thecatalyst to the desired temperature range.

In order to increase the efficiency of the system 10 of the presentinvention and maximize operational up time, a resin pre-heating coil 58may also be provided to facilitate the refilling of the resin tank 34while the system 10 is in operation. The resin preheat coil 58 extendsfrom the exterior of the tank 12 into the resin chamber 34 allows theresin 36 to be preheated before it is deposited into the resin chamber34. This allows the resin chamber 34 to be periodically refilled withouthaving to stop the application of the material while waiting for thenewly added resin 36 in the resin chamber 34 to preheat.

Turning now to FIG. 3, a schematic diagram is provided best illustratesthe operational method of the present invention. In general terms, thepresent invention provides a method of spray application for amulti-part epoxy material. Initially, the steps related to the handlingof the base resin 36 including the steps of: providing a heating tank 12with a resin chamber 34 therein; filling the resin chamber 34 with anepoxy resin 36; preheating the resin 36 within the resin chamber 34 to afirst temperature; and drawing said preheated resin 36 from said resinchamber 34 to create a resin flow 54. The steps related to the handlingof the catalyst include: providing a catalyst; creating a catalyst flow56; and preheating said catalyst flow 56 to a second temperature. Oncethe resin 54 and catalyst 56 flows have been preheated, the catalystflow 56 and said resin flow 54 are mixed and discharged at an elevatedpressure to a spray nozzle 20 for spray application.

Optionally, the method of the present invention may provide for heatingthe resin 36 material in two steps. As was stated above, in the firststep, the resin 36 in the resin tank 34 is initially heated to atemperature that allows the resin 36 to flow, but is well below theevaporation temperature of the various components within the resin 36.This prevents various chemical components within the base resin 36 fromflashing off, thereby changing the chemical composition andcharacteristics of the resin 36. In a second heating step, as the resin36 is being pumped out of the storage tank 34 it enters the resin heattransfer conduit 40 wherein the walls of the piping serve to contain theresin 36 in a closed environment while heating the resin 36 to thedesired application temperature of between approximately 150° F. and160°.

Clearly, the disclosure of the present invention provides that theheating tank 12 structure disclosed above with regard to the system 10is the same device that is employed in the method of the presentinvention for the purpose of heating the resin 36 and catalyst for eachof the various heating steps.

It can therefore be seen that the present invention provides a novelmethod and system for the spray application of epoxy materials thatresults in a substantial reduction in the viscosity of the materialwithout requiring the addition of VOC solvents. Further, the presentinvention provides a system for the spray application of epoxy materialsthat has dramatically increased efficiency with respect to the manner inwhich materials are handled as well as increased operational up time ascompared to the methods and systems known in the prior art. For thesereasons, the instant invention is believed to represent a significantadvancement in the art, which has substantial commercial merit.

While there is shown and described herein certain specific structureembodying the invention, it will be manifest to those skilled in the artthat various modifications and rearrangements of the parts may be madewithout departing from the spirit and scope of the underlying inventiveconcept and that the same is not limited to the particular forms hereinshown and described except insofar as indicated by the scope of theappended claims.

1. A system for the spray application of a multi-part epoxy material,said multi-part epoxy material including at least a resin and acatalyst, said system comprising: a heating tank, said heating tankincluding an outer wall and an inner wall, said inner wall having aninner surface and an outer surface, said outer wall and said outersurface of said inner wall cooperating to form a heating jackettherebetween, said inner surface of said inner wall forming a resinchamber, wherein said heating jacket contains a heat transfer medium,wherein said resin is contained within said resin chamber; means forheating said heat transfer medium disposed within said heating jacket; aresin heat transfer conduit disposed within said heating jacket, saidresin heat transfer conduit having an input end in fluid communicationwith said resin chamber and an output end disposed on the exterior ofsaid heating tank; a catalyst heat transfer conduit disposed within saidheating jacket said catalyst heat transfer conduit having an input endin fluid communication with a catalyst reservoir and an output enddisposed on the exterior of said heating tank; means for establishing aflow of resin through said resin heat transfer conduit; means forestablishing a flow of catalyst through said catalyst heat transferconduit; a mixing pump configured to receive and mix said flow of resinand said flow of catalyst and discharge said mixture at an elevatedpressure; and a spray applicator for applying said discharged mixture,wherein said heat transfer medium contains a detergent, a portion ofsaid heat transfer medium being used to flush said resin heat transferconduit, said catalyst heat transfer conduit, said mixing pump and saidspray applicator after discharging said mixture.
 2. The system of claim1, wherein said heat transfer medium is a mixture of water anddetergent.
 3. A method of spray application for a multi-part epoxymaterial, said multi-part epoxy material including at least a resin anda catalyst, said method comprising the steps of: providing a heatingtank having an outer wall, an inner wall, said inner wall having aninner surface forming a resin chamber and an outer surface, a heatingjacket disposed between said outer wall and said outer surface of saidinner wall, wherein said heating jacket contains a heat transfer mediumwherein said heat transfer medium contains a detergent, and means forheating said heat transfer medium disposed within said heating jacket;filling said resin chamber with an epoxy resin; preheating said resinwithin said resin chamber to a first temperature; drawing said preheatedresin from said resin chamber to create a resin flow; providing acatalyst; creating a catalyst flow; preheating said catalyst flow to asecond temperature; mixing said catalyst flow and said resin flow;discharging said mixed resin and catalyst flow at an elevated pressure;and employing portion of said heat transfer medium to flush said resinflow, said catalyst flow and said mixed resin and catalyst flow afterdischarging said mixed resin and catalyst flow.
 4. The system of claim3, wherein said heat transfer medium is a mixture of water anddetergent.